Could also use Awesome Blow, iirc, and do about the same thing.
Awesome blow is a standard action, so you can only perform 1 each round.
knockback has a minimum damage you have to break, as well, so there are tradeoffs.
To be honest, Knockback only requires you to succesfully hit your opponent.
Not damage him.
Sure, the more you draw upon Power Attack, the easier it will be to both hurt him and push him.
I've been through this over and over. I can't find anything that would prevent it.
I mean, if you're that cornered, that big hammer will make an impression on your organs each time it knocks you back into the wall, room for increased velocity or not.
Now I see why Dungeoncrashers get some love around here, I absolutely love this idea. It's soo cool.
Situational, but since when was a Barbarian/Fighter not situational?
Trippers can't trip everything.
Charge-builds need clear lanes.
Intimidating-build might encounter fear-immune critters.
Etc.
I think a Goliath Dungeoncrasher 6 would make a good character in E6.
Power Attack, Improved Bullrush, Cleave, Improved Sunder, Weapon Focus: Heavy Mace, Combat Brute, Shocktrooper, Three Mountains [Style], Knockback, Auspicious Marking, Markings of the Blessed/Hunter/Warrior. Certanly a feat-heavy build with good damage potential for it's level.